There is an interpolation filter used in H.264/MPEG-4AVC (hereinafter referred to as H.264), i.e., one of international standard specifications of video encoding as an interpolation filter used for motion compensation of sub-pixel precision. In the H.264 interpolation filter, first, a pixel value of a half pixel is calculated, and a pixel value of a quarter pixel is calculated from an average of the calculated half pixels.
In addition, there is another interpolation filter, in which, first, a value calculated by applying a filter in a first direction is subjected to round off processing, whereby a reference value serving as a basis of a sub-pixel is calculated, and then, using the calculated reference value, a filter is applied in a second direction different from the first direction, and further, round off processing is performed to generate sub-pixels (See, e.g., Jpn. PCT National Publication No. 2008-507190).
Still further, there is an adaptive loop filter (ALF), i.e., another method for improving prediction efficiency by motion compensation. In the ALF, filter information including filter coefficients designed by an encoding side is sent to a decoding side, and the image quality is improved by using a common loop filter both in the encoding and decoding sides (See, e.g., T. Chujoh, N. Wada, G. Yasuda, “Quadtree-based Adaptive Loop Filter,” ITU-T Q.6/SG16 Doc., C181, Geneva, January 2009).